Optimization for rendering web pages

ABSTRACT

In one embodiment, there is provided a method for rendering a web page. The method comprises parsing a Hypertext Markup Language (HTML) document for a web page to generate a Document Object Model (DOM) tree. The method further comprises rendering elements in the DOM tree in a higher-to-lower sequence based on their z-index attributes from a style sheet corresponding to the HTML document. The method further comprises skipping rendering for an element with a lower z-index attribute than an element with a higher z-index attribute if the element with the lower z-index attribute is below the element with the higher z-index attribute and would not be seen by a user viewing the web page.

BACKGROUND

The present invention relates to web page rendering, and morespecifically, to optimization for rendering web pages.

Nowadays, Web 2.0 is becoming more popular, and browsers are facing moredifficulties in rendering entire web pages, especially complex Web 2.0application pages. Current rendering mechanisms of web browserstypically are not well suited for Web 2.0 single page applications(SPA), which typically include lots of Hypertext Markup Language (HTML),Cascading Style Sheets (CSS) and JavaScript together.

Traditional web applications can cause disruption in user experience andworkflow. For example, traditional web applications work by reloadingthe entire web page. In order to advance through a workflow, the userinteracts with page elements (such as hyperlinks and form submitbuttons) that cause the browser to issue a request to the server for acompletely new page. Continual page redraws disrupt the user experiencebecause the network latencies cannot be hidden from the user. There istypically a perceivable transitional jolt from one page to the next.Data of the next page is retrieved from the server, the old page isunloaded, and the new page is rendered to screen. The complete pagereload that occurs on each user interaction results in unnecessaryre-transmission of data over the network. This can make the overallperformance of the website slower.

A single page application (SPA), also known as single page interface(SPI), is a web application that fits on a single web page with the goalof providing a more fluid user experience akin to a desktop application.SPAs address the above issues by requiring no page reload by the browserduring an application session. All user interaction and changes of theapplication state are handled in the context of a single Web document.The user experience becomes more continuous and fluid, and networklatencies can be hidden more easily.

In a SPA, either all necessary code (HTML, JavaScript, and CSS) isretrieved with a single page load, or partial changes are performedwhich load new code on demand from the web server, usually driven byuser actions. The page is not automatically reloaded during userinteraction with the application, and control is not transferred toanother page. Updates to the displayed page may or may not involveinteraction with a server. Thus, compared to normal Web applicationsthat still use URL to switch between various functions and pages, thesingle page application achieves transferring of Web applicationprograms from server side to client side, i.e., to browsers. Thismechanism brings an additional advantages of cost reduction in servers,in addition to improvements in interactivity and response speed that canbe perceived by users, and lower bandwidth occupancy between servers andclients.

However, since for SPA the Web application is transferred to clientside, i.e., to a browser, the performance of the browser becomesimportant. For example, time cost on the first time rendering for a SPAweb page is large, and frequent reflow and repaint via user behaviorwith respect to the SPA web page will bring bad performance.

Currently, there are several commonly used ways to improve theperformance of a browser, one of which is to perform a reflow only whensome reflow condition is matched, instead of performing the reflowunconditionally.

SUMMARY

Considering the above problems, embodiments of the present inventionprovide methods and systems for rendering a web page in a browser withimproved performance.

According to an embodiment of the present invention, a method forrendering a web page is provided, comprising: parsing a Hypertext MarkupLanguage (HTML) document for a web page to generate a Document ObjectModel (DOM) tree; rendering elements in the DOM tree in ahigher-to-lower sequence based on their z-index attributes from a stylesheet corresponding to the HTML document; and skipping rendering for anelement with a lower z-index attribute than an element with a higherz-index attribute if the element with the lower z-index attribute isbelow the element with the higher z-index attribute and would not beseen by a user viewing the web page.

According to another embodiment of the present invention, a system forrendering a web page is provided, comprising: one or more computerprocessors; one or more computer readable storage media; and programinstructions stored on the one or more computer readable storage mediafor execution by at least one of the one or more processors to performactions of: parsing a Hypertext Markup Language (HTML) document for aweb page to generate a Document Object Model (DOM) tree; renderingelements in the DOM tree in a higher-to-lower sequence based on theirz-index attributes from a style sheet corresponding to the HTMLdocument; and skipping rendering for an element with a lower z-indexattribute than an element with a higher z-index attribute if the elementwith the lower z-index attribute is below the element with the higherz-index attribute and would not be seen by a user viewing the web page.

According to another embodiment of the present invention, a computerprogram product for rendering a web page is provided, the computerprogram product comprising one or more computer readable storage mediaand program instructions stored on the one or more computer readablestorage media, the program instructions being executable by one or morecomputer processors to perform actions of: parsing a Hypertext MarkupLanguage (HTML) document for a web page to generate a Document ObjectModel (DOM) tree; rendering elements in the DOM tree in ahigher-to-lower sequence based on their z-index attributes from a stylesheet corresponding to the HTML document; and skipping rendering for anelement with a lower z-index attribute than an element with a higherz-index attribute if the element with the lower z-index attribute isbelow the element with the higher z-index attribute and would not beseen by a user viewing the web page.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary computer system which is applicable toimplement embodiments of the present invention;

FIG. 2 shows a flowchart illustrating a method for rendering a web pageaccording to an embodiment of the present invention;

FIG. 3 shows an example of a DOM tree generated according to anembodiment of the present invention; and

FIG. 4 shows an example layout on a browser of elements in the generatedDOM tree of FIG. 3, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION

Some preferable embodiments will be described in more detail withreference to the accompanying drawings, in which the preferableembodiments of the present disclosure have been illustrated. However,the present disclosure can be implemented in various manners, and thusshould not be construed to be limited to the embodiments disclosedherein. On the contrary, those embodiments are provided for the thoroughand complete understanding of the present disclosure, and completelyconveying the scope of the present disclosure to those skilled in theart.

Referring now to FIG. 1, in which an exemplary computer system/server 12which is applicable to implement the embodiments of the presentinvention is shown. Computer system/server 12 is only illustrative andis not intended to suggest any limitation as to the scope of use orfunctionality of embodiments of the invention described herein.

As shown in FIG. 1, computer system/server 12 is shown in the form of ageneral-purpose computing device. The components of computersystem/server 12 may include, but are not limited to, one or moreprocessors or processing units 16, a system memory 28, and a bus 18 thatcouples various system components including system memory 28 toprocessor 16.

Bus 18 represents one or more of any of several types of bus structures,including a memory bus or memory controller, a peripheral bus, anaccelerated graphics port, and a processor or local bus using any of avariety of bus architectures. By way of example, and not limitation,such architectures include Industry Standard Architecture (ISA) bus,Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, VideoElectronics Standards Association (VESA) local bus, and PeripheralComponent Interconnect (PCI) bus.

Computer system/server 12 typically includes a variety of computersystem readable media. Such media may be any available media that isaccessible by computer system/server 12, and it includes both volatileand non-volatile media, removable and non-removable media.

System memory 28 can include computer system readable media in the formof volatile memory, such as random access memory (RAM) 30 and/or cachememory 32. Computer system/server 12 may further include otherremovable/non-removable, volatile/non-volatile computer system storagemedia. By way of example only, storage system 34 can be provided forreading from and writing to a non-removable, non-volatile magnetic media(not shown and typically called a “hard drive”). Although not shown, amagnetic disk drive for reading from and writing to a removable,non-volatile magnetic disk (e.g., a “floppy disk”), and an optical diskdrive for reading from or writing to a removable, non-volatile opticaldisk such as a CD-ROM, DVD-ROM or other optical media can be provided.In such instances, each can be connected to bus 18 by one or more datamedia interfaces. As will be further depicted and described below,memory 28 may include at least one program product having a set (e.g.,at least one) of program modules that are configured to carry out thefunctions of embodiments of the invention.

Program/utility 40, having a set (at least one) of program modules 42,may be stored in memory 28 by way of example, and not limitation, aswell as an operating system, one or more application programs, otherprogram modules, and program data. Each of the operating system, one ormore application programs, other program modules, and program data orsome combination thereof, may include an implementation of a networkingenvironment. Program modules 42 generally carry out the functions and/ormethodologies of embodiments of the invention as described herein.

Computer system/server 12 may also communicate with one or more externaldevices 14 such as a keyboard, a pointing device, a display 24, etc.;one or more devices that enable a user to interact with computersystem/server 12; and/or any devices (e.g., network card, modem, etc.)that enable computer system/server 12 to communicate with one or moreother computing devices. Such communication can occur via Input/Output(I/O) interfaces 22. Still yet, computer system/server 12 cancommunicate with one or more networks such as a local area network(LAN), a general wide area network (WAN), and/or a public network (e.g.,the Internet) via network adapter 20. As depicted, network adapter 20communicates with the other components of computer system/server 12 viabus 18. It should be understood that although not shown, other hardwareand/or software components could be used in conjunction with computersystem/server 12. Examples, include, but are not limited to: microcode,device drivers, redundant processing units, external disk drive arrays,RAID systems, tape drives, and data archival storage systems, etc.

In prior art systems, after inputting a URL of a web page, a browserlocated at a client device typically receives an HTML document and astyle sheet from a server addressed by the URL, wherein the HTMLdocument includes elements in the web pages, and the style sheetincludes attributes specifying the styles of each of the elements. AnHTML parser of the browser is used to parse the received HTML documentinto a Document Object Model (DOM) tree. All of the elements in the HTMLare created in the DOM tree as nodes. DOM actually is a document modeldescribed in an object oriented manner. DOM defines objects necessaryfor representing and modifying a document, behaviors and attributes ofthese objects, and relationship between these objects. DOM can be deemedas a tree representation of data and structures on a page. Afterobtaining the DOM tree or at the same time, a CSS parser of the browseris used to parse the received style sheet into style rules, whichdefines attributes specifying the styles of each of the elements.

The parsed DOM tree and the parsed style rules can then be used by thebrowser to render the web page. Specifically, the process of renderingincludes layout computing (also known as reflow) and painting (alsoknown as repaint) of the elements. Each of the elements in the DOMstructure has its own box (model), which needs to be computed by thebrowser according to various styles of browsers or defined by adeveloper, and elements will be put in place according to the result ofthe computation. This process is called “reflow”. In other words, reflowrefers to a process of calculating position and geometry of an elementin a document by a browser for rendering part or the whole of thedocument. After positions, sizes and other attributes such as color,font, etc. of various boxes are determined, the browser paints theseelements according to their respective styles so that content of the webpage is presented. This process is called “repaint”.

Reflow and repaint must happen while loading a web page. In addition,after the loading of the web page, some operations of a user or someoperations of a script may also cause a reflow and/or a repaint in abrowser. For example, resizing the window of a browser, using some JavaScript methods (including computing styles, changing class of anelement, or adding or deleting an element in a DOM tree) will cause areflow; changing color of an element and changing font of an elementwill cause a repaint only. Sometimes, even if reflow is needed for onlyone element, it might require reflow for its parent element, grandparentelement, and any child elements.

In the prior art, during the rendering, the layout computing isperformed to all elements in the HTML document, and thereafter elementsare painted one by one according to their styles.

An aspect of the invention provides a new method for a browser to do therendering phase for a complex single page application, and describes adifferent approach in handling rendering workflow of a browser. Thisapproach can help to build a more powerful browser rendering engine withbetter performance.

FIG. 2 shows a flowchart illustrating a method 200 for rendering a webpage according to an embodiment of the present invention. As shown inFIG. 2, the method 200 includes a parsing step 210, a rendering step 220and a skipping step 230. Hereinafter, respective steps of the method 200will be explained in detail.

In the parsing step 210, an HTML document is parsed to generate a DOMtree. In one embodiment of the invention, the parsing is performed by anHTML parser of a browser, and the HTML document is received from aserver in response to an access request for a web page by the browser.After the parsing, all elements in the HTML documents are formed in theDOM tree as nodes, and all of the elements will be rendered.

In a modification of the parsing step 210 according to another aspectthe invention, the parsing includes parsing with reference to a set ofattributes from the style sheet corresponding to the HTML document sothat the DOM tree is generated with hidden elements being separated fromother elements. As described above, the style sheet includes attributesspecifying the styles of each of the elements in the web page. Here,hidden elements refers to elements outside of the viewport of thebrowser, or elements inside the viewport of the browser but having anattribute “display” with a value of “none” or an attribute “visibility”with a value of “hidden”. In a further embodiment of the invention, anelement having attribute “opacity” with a value of “0” can also bedeemed as a hidden element since this element is completely transparent.For those hidden elements, since they cannot be seen and cannotinfluence the layout or the appearance of the web page, effort taken forrendering them in loading the web page at the first time is wasteful,and, thus, hidden elements can be filtered out before rendering toimprove the performance of rendering.

To filter hidden elements out, the HTML parser refers to the stylerules. Here, a specific example is given to explain how to use stylerules to filter hidden elements out. The following is an example of aCSS source file:

body .edit {  background-image: url(‘/demandtec/images/dojo/edit.gif’); width: 25px;  height: 16px;  z-index: 50;  position: absolute; left:50px; top: 50px; } #container .dijitMenuItemSelected .innerContainer >.editButton {  display: none;  border: 1px solid red; } .deleteButton { opacity: 0.9;  z-index: 100;  padding: 5px; }

In this example CSS source file, styles of three elements (i.e., (body.edit), (#container.dijitMenultemSelected.innerContainer>.editButton),and (.deleteButton)) are defined. Typically, the CSS source file isprocessed by a CSS parser of the browser to create a map consists ofpairs of keys and values. Specifically, each key corresponds to anelement, and the value corresponds to all attributes of the element. Forexample, a pair in the map could be: .deleteButton->opacity: 0.9;z-index: 100; padding: 5px. This map will help the browser to render aweb page based on elements in the web page.

However, in the modification of the parsing step 210, in addition to theabove map, a new map is created for use in the parsing in the HTMLparser. The new map also consists of pairs of keys and values; however,in the new map, each key corresponds to one of a set of attributes, andthe value corresponds to elements having the attribute. The set ofattributes include at least one of visibility, display, attributesrelated to position, attributes related to transform, attributes relatedto perspective, and opacity. For example, attributes such as position,left, top right, bottom, width, height, etc. belong to attributesrelated to position. Attributes related to transform and attributesrelated to perspective are defined by CSS3. The attributes in the setused as keys in the new map are not limited by the above examples. Anyattribute that can be used to identify if an element is actually visibleto a viewer can be used as a key in the new map, which includesattributes that may emerge in further versions of CSS. The z-indexattribute indicates a depth of an element in the meaning of graphics.The higher the z-index of an element is, the closer the element is tothe viewer in the depth direction. However, those skilled in the artknow that the z-index does not represent a real depth, and it onlyrepresents an overlaying relationship between elements. The z-index isdifferent from the above set of attributes since z-index cannot be usedto identify if an element is actually visible to a viewer. In oneembodiment of the invention, z-index is used to organize elements otherthan the hidden elements.

For example, for the above CSS source file, a new map can be created asfollows:

Key Value position −> (body .edit) display −> (#container.dijitMenuItemSelected .innerContainer > .editButton) z-index −> (body.edit) + (.deleteButton)

With this new map, since keys in the new map are attributes, it will behelpful for the HTML parser to generate a DOM tree based on specificattributes. In one embodiment of the invention, the new map can becreated directly from the CSS source file. In another embodiment of theinvention, the new map can be created from the style rules, i.e., theresult obtained by the CSS parser parsing the CSS source file.

In the modification of the parsing step 210, the parsing includesparsing with reference to a set of attributes from the style sheetcorresponding to the HTML document, so that the DOM tree is generatedwith hidden elements being separated from other elements. FIG. 3 showsan example of a DOM tree generated according to an embodiment of theinvention, which is used to explain how to separate hidden elements fromother elements in generating the DOM tree. FIG. 4 shows an examplelayout on the browser of elements in the generated DOM tree of FIG. 3.

In FIG. 3, a DOM tree generated by the HTML parser according to anembodiment of the invention is illustrated, in which an oval representsa node of the DOM tree (3000, 3101-3104, 3201-3203, 3311, 3321-3322,3331-3334), and a box represents a condition used to determine whichelement(s) should be put in the branch corresponding to the box (3100,3200, 3300, 3310, 3320, 3330). For example, elements having an attributesatisfying “display: none” or “visibility: hidden” will be placed in the“display & visibility” branch of the DOM tree. If an element has anattribute of “display: none”, the element will not be displayed. If anelement has an attribute of “visibility: hidden”, the element will behidden. Thus, it will save effort and improve performance if theseelements are filtered out before rendering. In FIG. 3, for example,elements div1 and div2 have an attribute of “display: none”, andelements tabcontainer_div_2 and tabcontainer_div_3 have an attribute of“visibility: hidden”, thus they are placed in the “display & visibility”branch. FIG. 4 shows the position of elements div1 and div2, andelements div1 and div2 will not be displayed. In FIG. 4, elementstabcontainer_div1, tabcontainer_div_2 and tabcontainer_div_3 form athree-tab control on the web page. After rendering, the tab oftabcontainer_div_1 is shown by default, and the other two tabs arehidden and cannot be seen.

Additionally, for example, elements that have been determined to beoutside of the viewport of the browser are placed in the “out ofviewport” branch of the DOM tree. For example, the determination can bebased on attributes related to position, attributes related totransform, attributes related to perspective, etc. of an element. If anelement is determined to be outside of the viewport of the browser basedon its attributes, filtering out that element before rendering will saveeffort and improve performance. In FIG. 3, for example, element div3,div4 and div5 are determined to be outside of the viewport of thebrowser based on their attributes, so they are place in the “out ofviewport” branch of the DOM tree. FIG. 4 shows the position of elementsdiv3, div4 and div5 (i.e., outside of viewport), and elements div3, div4and div5 will not be seen.

In the example of FIG. 3, elements in the “out of viewport” branch andthe “display & visibility” branch of the DOM tree belong to hiddenelements. Elements other than the hidden elements are organized inanother branch. Thus, the hidden elements and elements other than thehidden elements are separated from each other in the DOM tree. In oneembodiment of the invention, elements with different z-index attributesare located in different parts of the DOM tree. That is, besides beingplaced together, for example in the same branch, elements other thanhidden elements are further organized based on their z-index attribute.In the example of FIG. 3, elements other than hidden elements are allplaced in the “z-index” branch and further organized based on z-indexattribute of the elements. For example, element div100 is placed in the“100” branch since it has an attribute of “z-index: 100”; elements div50and div51 are placed in the “50” branch since they have an attribute of“z-index: 50”; and elements tabcontainer_div_1, div6, div7 and div8 areplaced in the “0” branch since they have an attribute of “z-index: 0” ordo not define the z-index attribute.

FIG. 3 only shows an exemplary structure of a DOM tree. The invention isnot limited by the example in FIG. 3. For example, hidden elements canbe organized in only one branch, or hidden elements can be organized inthree or more branches, such as “display” branch, “visibility” branch,“out of viewport: position” branch, “out of viewport: transform” branch,“out of viewport: perspective” branch, etc. The hidden elements can beorganized in any manner in which they are separated from non-hiddenelements. In another embodiment of the invention, elements are justplaced together in the DOM tree but not organized based on z-indexattributes, in which case the HTML parser will search through thenon-hidden elements for an element with the highest z-index, then anelement with the second highest z-index, etc.

Now returning to FIG. 2, in the rendering step 220, elements in the DOMtree are rendered in a higher-to-lower sequence based on their z-indexattributes from a style sheet corresponding to the HTML document. In oneembodiment of the parsing step 210, elements are not treateddifferently, so all elements will be rendered in the rendering step 220in a higher-to-lower sequence based on their z-index attributes. Thatis, the element with the highest z-index will be rendered first, and theelement with the lowest z-index will be rendered last.

However, if the modification of the parsing step 210 is adopted, onlyelements other than hidden element (elements after filtering) will berendered. That is, in the rendering step 220, the rendering includesonly rendering elements other than the hidden element. Taking the DOMtree in FIG. 3 as an example, element div 100 will be rendered firstsince it has the highest z-index of “100”; then elements div50 and div51are to be rendered since they have the second highest z-index of “50”;and then elements tabcontainer_div_1, div6, div7 and div8 are to berendered last since they have the lowest z-index of “0”.

In the skipping step 230, the rendering for an element with a lowerz-index attribute is skipped if the element with a lower z-indexattribute is below an element with a higher z-index attribute and cannotbe seen (i.e., would not be seen by a user viewing the rendered webpage). During the rendering step, elements in the DOM tree areconsidered from upper level to lower level. After rendering an upperelement, it needs to be determined if a lower element is completelycovered by the upper element based on their position related attributes.If an element cannot be seen, then that element is completely covered byan upper nontransparent element. This process will be explained withreference to the examples in FIG. 3 and FIG. 4. For example, in FIG. 4,element div100 with z-index of “100” is rendered first.

After that, elements div50 and div51 with z-index of “50” are to berendered. Since element div50 is not below any upper elements, it willbe rendered. However, for element div51, it is determined that elementdiv51 is below the upper element div100 based on their position relatedattributes. Here, if element div51 is overlapped with element div100,but not completely covered by element div100, then element div51 stillcan be seen, and, thus, element div51 will be rendered. However, ifelement div51 is completely covered by element div 100, as shown in FIG.4, the opacity attribute of the upper element (i.e., div100) should beconsidered. If the opacity attribute of element div100 is less than 1,which means it is transparent to some extent, then element div51 stillcan be seen, and, thus, element div51 will be rendered. Otherwise, ifthe opacity attribute of element div100 is equal to 1, which means it isnot transparent completely, then rendering for element div51 can beskipped.

After that, elements tabcontainer_div_1, div6, div7 and div8 withz-index of “0” are to be rendered. Since element tabcontainer_div_1 isnot below any upper elements, it will be rendered. However, for elementsdiv6, div7 and div8, it is determined that element div6 is below theupper element div50, and elements div7 and div8 are below the upperelement div100, based on their position related attributes. Thus, forelements div6, div7 and div8, a determination needs to be made similarto the above determination on element div51.

Here, in FIG. 4, it is assumed that the opacity attribute of elementdiv100 has a value of “1” and the opacity attribute of element div50 hasa value of “0.5”. In this case, element div6 can be seen and, thus, isrendered; and elements div51, div7 and div8 are covered completely byelement div100 that are not transparent, thus the rendering for elementsdiv51, div7 and div8 is skipped. The skipping will save effort forrendering unnecessary elements and improve the rendering performance ofthe browser.

As described above, after the loading of the web page, some operationsof a user or some operations of a script will also cause a reflow and/ora repaint in a browser. In one embodiment of the invention, the method200 may further comprise: in response to a change of the DOM tree,rendering elements in the changed DOM tree in a higher-to-lower sequencebased on their z-index attributes; and skipping the rendering for anelement in the changed DOM tree with a lower z-index attribute if theelement with a lower z-index attribute is below an element with a higherz-index attribute and cannot be seen. That is, the processes in steps220 and 230 of the method 200 will be performed in response to a changeof the structure of the DOM tree.

As for the example in FIG. 3, if a user clicks the second tab(tabcontainer_div_2) on the web page, the attribute “visibility” ofelement tabcontainer_div_2 will become “visible” from “hidden”, andaccordingly the attribute “visibility” of element tabcontainer_div_1will become “hidden” from “visible”. Thus, the change of style willcause the change of DOM tree. In this case, in response to the useroperation, positions of elements tabcontainer_div_1 andtabcontainer_div_2 in the DOM tree are swapped. Now, rendering forelements is performed based on the modified DOM tree in ahigher-to-lower sequence based on their z-index attributes. The processof rendering and skipping is similar to that in the steps 220 and 230.

In another example, if a user operation or running of a script causeselement div100 to be removed from the DOM tree, then the rendering isperformed based on the modified DOM tree in a higher-to-lower sequencebased on their z-index attributes. In this example, since the upperelement div100 is removed, elements div7, div8 and div51 can now beseen, and, thus, will be determined to be rendered.

Reflow and repaint are associated with each other. Reflow involveslayout computing (i.e., the updating of data). Repaint involvespresentation (i.e., actual painting). In prior art systems, a reflowwill typically cause a repaint. In some cases, user operations arefrequent, which will cause a frequent reflow and repaint. Typically, thepainting will cost much more time than layout computing.

In another embodiment of the invention, to further improve theperformance of the browser, the method 200 may further comprise:performing layout computing once the layout of an element changes,during the running of a JavaScript thread initiated automatically or inresponse to a user operation on the web page; and painting all of theelements whose layouts have changed at once, based on the final resultof the layout computing, in the JavaScript thread. That is, thisembodiment splits the reflow (model) and repaint (presentation), thus areflow will not necessarily cause a repaint. Specifically, a JavaScriptthread will be initiated automatically or in response to a useroperation on the web page. During the running of this JavaScript thread,layout computing (reflow) is performed once the layout of an elementchanges (i.e., the layout computing can be performed multiple timesaccumulatively). However, the painting of all of the elements whoselayouts have changed will be performed only once during the running, orat the end, of this JavaScript thread. By doing so, the painting thatconsumes much time will not be performed too frequently, and, thus, theperformance of the browser can be improved further.

In another embodiment of the invention, to further improve theperformance of the browser, the method 200 may further comprise: cachingdata for rendering a part of elements in the DOM tree based on theanalysis of user operations on the web page; and using cached data toperform layout computing and painting of the part of elements when theyare to be rendered. This process will be explained with reference toFIG. 3 and FIG. 4. Firstly, the history of user operation can beanalyzed to identify a frequent user operation. For example, if the userfrequently clicked the third tab (tabcontainer_div_3) on the web page inFIG. 4, then data for rendering the third tab can be cached. The datafor rendering may include result of layout computing, or anyintermediate data structure that can accelerate the rendering. When anelement whose data for rendering is cached is to be rendered, the cacheddata can be used to perform layout computing and painting of theelement. Since cached data is used, it is not necessary to performlayout computing and painting for a frequently rendered element all thetime, and the performance of the browser is further improved.

With the above embodiments of the invention, better performance for anSPA web page and better performance for reflow and repaint are achieved.In addition to browsers, embodiments of the present invention also applyto apps and other computer software that are based on Web 2.0.

The present invention may be a system, a method, and/or a computerprogram product. The computer program product may include a computerreadable storage medium (or media) having computer readable programinstructions thereon for causing a processor to carry out aspects of thepresent invention.

In an embodiment of the present invention, there is provided a computerprogram product for rendering a web page. The computer program productcomprises a computer readable storage medium having program instructionsembodied therewith. The program instructions are executable by a deviceto perform a method. The method comprises parsing an HTML document togenerate a DOM tree. The method further comprises rendering elements inthe DOM tree in a higher-to-lower sequence based on their z-indexattributes corresponding to the HTML document. The method furthercomprises skipping the rendering for an element with a lower z-indexattribute if the element with a lower z-index attribute is below anelement with a higher z-index attribute and cannot be seen.

In one embodiment of the computer program product, wherein the parsingincludes parsing with reference to a set of attributes from the stylesheet corresponding to the HTML document so that the DOM tree isgenerated with hidden elements being separated from other elements; andwherein the rendering includes only rendering elements other than thehidden element.

In one embodiment of the computer program product, wherein the set ofattributes include at least one of visibility, display, attributesrelated to position, attributes related to transform, attributes relatedto perspective, and opacity.

In one embodiment of the computer program product, wherein the renderingincludes layout computing and painting of the elements, and wherein themethod further comprising: performing layout computing once the layoutof an element changes, during the running of a JavaScript threadinitiated automatically or in response to a user operation on the webpage; and painting all of the elements whose layouts have changed atonce, based on the final result of the layout computing, in theJavaScript thread.

In one embodiment of the computer program product, wherein the methodfurther comprising: in response to a change of the DOM tree or style ofan element, rendering elements in the DOM tree in a higher-to-lowersequence based on their z-index attributes; and skipping the renderingfor an element with a lower z-index attribute if the element with alower z-index attribute is below an element with a higher z-indexattribute and cannot be seen.

In one embodiment of the computer program product, wherein the methodfurther comprising: caching data for rendering a part of elements in theDOM tree based on the analysis of user operations on the web page; andusing cached data to perform layout computing and painting of the partof elements when they are to be rendered.

The computer readable storage medium can be a tangible device that canretain and store instructions for use by an instruction executiondevice. The computer readable storage medium may be, for example, but isnot limited to, an electronic storage device, a magnetic storage device,an optical storage device, an electromagnetic storage device, asemiconductor storage device, or any suitable combination of theforegoing. A non-exhaustive list of more specific examples of thecomputer readable storage medium includes the following: a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), a static random access memory (SRAM), a portablecompact disc read-only memory (CD-ROM), a digital versatile disk (DVD),a memory stick, a floppy disk, a mechanically encoded device such aspunch-cards or raised structures in a groove having instructionsrecorded thereon, and any suitable combination of the foregoing. Acomputer readable storage medium, as used herein, is not to be construedas being transitory signals per se, such as radio waves or other freelypropagating electromagnetic waves, electromagnetic waves propagatingthrough a waveguide or other transmission media (e.g., light pulsespassing through a fiber-optic cable), or electrical signals transmittedthrough a wire.

Computer readable program instructions described herein can bedownloaded to respective computing/processing devices from a computerreadable storage medium or to an external computer or external storagedevice via a network, for example, the Internet, a local area network, awide area network and/or a wireless network. The network may comprisecopper transmission cables, optical transmission fibers, wirelesstransmission, routers, firewalls, switches, gateway computers and/oredge servers. A network adapter card or network interface in eachcomputing/processing device receives computer readable programinstructions from the network and forwards the computer readable programinstructions for storage in a computer readable storage medium withinthe respective computing/processing device.

Computer readable program instructions for carrying out operations ofthe present invention may be assembler instructions,instruction-set-architecture (ISA) instructions, machine instructions,machine dependent instructions, microcode, firmware instructions,state-setting data, or either source code or object code written in anycombination of one or more programming languages, including an objectoriented programming language such as Smalltalk, C++ or the like, andconventional procedural programming languages, such as the “C”programming language or similar programming languages. The computerreadable program instructions may execute entirely on the user'scomputer, partly on the user's computer, as a stand-alone softwarepackage, partly on the user's computer and partly on a remote computeror entirely on the remote computer or server. In the latter scenario,the remote computer may be connected to the user's computer through anytype of network, including a local area network (LAN) or a wide areanetwork (WAN), or the connection may be made to an external computer(for example, through the Internet using an Internet Service Provider).In some embodiments, electronic circuitry including, for example,programmable logic circuitry, field-programmable gate arrays (FPGA), orprogrammable logic arrays (PLA) may execute the computer readableprogram instructions by utilizing state information of the computerreadable program instructions to personalize the electronic circuitry,in order to perform aspects of the present invention.

Aspects of the present invention are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer readable program instructions.

These computer readable program instructions may be provided to aprocessor of a general purpose computer, special purpose computer, orother programmable data processing apparatus to produce a machine, suchthat the instructions, which execute via the processor of the computeror other programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks. These computer readable program instructionsmay also be stored in a computer readable storage medium that can directa computer, a programmable data processing apparatus, and/or otherdevices to function in a particular manner, such that the computerreadable storage medium having instructions stored therein comprises anarticle of manufacture including instructions which implement aspects ofthe function/act specified in the flowchart and/or block diagram blockor blocks.

The computer readable program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other deviceto cause a series of operational steps to be performed on the computer,other programmable apparatus or other device to produce a computerimplemented process, such that the instructions which execute on thecomputer, other programmable apparatus, or other device implement thefunctions/acts specified in the flowchart and/or block diagram block orblocks. The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method for rendering a web page, comprising:parsing a Hypertext Markup Language (HTML) document for a web page togenerate a Document Object Model (DOM) tree; rendering elements in theDOM tree in a higher-to-lower sequence based on their z-index attributesfrom a style sheet corresponding to the HTML document; and skippingrendering for an element with a lower z-index attribute than an elementwith a higher z-index attribute if the element with the lower z-indexattribute is below the element with the higher z-index attribute andwould not be seen by a user viewing the web page.
 2. The methodaccording to claim 1, wherein the parsing includes parsing the HTMLdocument with reference to a set of attributes from the style sheetcorresponding to the HTML document so that the DOM tree is generatedwith hidden elements being separated from other elements; and whereinthe rendering includes only rendering elements other than the hiddenelements.
 3. The method according to claim 2, wherein the set ofattributes includes at least one of visibility, display, attributesrelated to position, attributes related to transform, attributes relatedto perspective, or opacity.
 4. The method according to claim 1, whereinthe rendering includes layout computing and painting of elements in theDOM tree.
 5. The method according to claim 4, further comprising:performing layout computing once a layout of an element changes, duringrunning of a JavaScript thread initiated automatically or in response toa user operation on the web page; and painting all elements whoselayouts have changed at once, based on a final result of the layoutcomputing, in the JavaScript thread.
 6. The method according to claim 1,further comprising: in response to a change of the DOM tree, renderingelements in the changed DOM tree in a higher-to-lower sequence based ontheir respective z-index attributes; and skipping rendering for anelement in the changed DOM tree with a lower z-index attribute than anelement with a higher z-index attribute if the element with the lowerz-index attribute is below the element with the higher z-index attributeand would not be seen by a user viewing the web page.
 7. The methodaccording to claim 4, further comprising: caching data for renderingportion of elements in the DOM tree based on an analysis of useroperations on the web page; and using the cached data to perform layoutcomputing and painting of the part of elements when the portion ofelements are to be rendered.